In devices that use a battery as a drive power source, such as electric bicycles, electric motorcycles, and electric cars, a battery pack that houses large-capacity secondary batteries is used. Lithium-ion batteries that are high in both volumetric energy density and mass energy density are suitable as drive-power-source batteries.
Among the known lithium-ion batteries are a columnar battery, which is made by winding up a laminated product in which a positive electrode and a negative electrode are stacked through a separator, and a flat battery, which is a laminated product in which a positive electrode and a negative electrode are stacked through a separator.
Among those batteries, the flat battery is suitable as a power-source battery for a power motor and the like, because the capacity can be easily increased per unit battery by increasing the areas of the positive and negative electrodes or by increasing the number of positive and negative electrodes stacked.
In a unit battery of a flat-type lithium-ion battery, a battery element is covered with a film exterior material. Therefore, it is possible to make effective use of high energy density that the lithium-ion battery has.
What has been proposed is a battery pack that includes a battery module in which a film-covered battery, whose positive- and negative-electrode pull-out tabs have been pulled out from sides of the battery that face each other, is stacked as a peripheral heat-sealing portion is held by a frame-like member in which an opening is provided in a portion corresponding to a power generation element (Refer to Patent Document 1, for example).